1. Technical Field
The present invention relates generally to a fuel injection system for internal combustion engines, and particularly to a common rail fuel injection system for diesel engines which may be employed in automotive vehicles.
2. Background Art
Typical fuel injection systems for internal combustion engines need to control the amount of fuel discharged from a fuel feed pump finely to supply a required amount of fuel to the internal combustion engine. Specifically, the fuel injection systems determine a target amount of fuel (i.e., a target flow rate of fuel) to be supplied to the engine in the next cycle based on current operating conditions of the engine and control an operation of a fuel injector to achieve the target amount of fuel.
The quantity of fuel to be sprayed from the fuel injector usually depends greatly upon the pressure of fuel at an on-time when the fuel injector is opened. The fuel injection systems, therefore, regulate the amount of fuel to be discharged from the pump based on the operating conditions of the engine to bring the pressure of fuel into agreement with a target level. For instance, Japanese Patent First Publication No. 3-18645 teaches such a fuel injection system.
Generally, the operation of the pump of the fuel injection systems is controlled based on a discharged pressure of fuel (i.e., the pressure of fuel at an outlet of the pump). The fuel injection systems usually have a pressure sensor installed in a portion of a high-pressure fuel path which is closer to the fuel injector than to the outlet of the pump, which will lead to the high probability that the pressure of fuel, as measured by the pressure sensor is different from that of fuel discharged actually from the pump.
Specifically, the pressure of fuel at the outlet of the pump usually starts to rise at the moment the fuel is discharged from the pump, but it is impossible for the pressure sensor to measure such a pressure change until it propagates to the pressure sensor. Therefore, when the pressure of fuel discharged from the pump is changing momentarily, it almost results in a difference between the pressure of fuel, as measured by the pressure sensor, and that of fuel discharged actually from the pump.
The fine control of the quantity of fuel to be sprayed from the fuel injector, however, requires accurate measurement of the pressure of fuel in the fuel injector. The installation of the pressure sensor at the outlet of the pump will, therefore, result in an error in measuring the pressure of fuel due to the propagation of the pressure of fuel, as described above.